The present invention pertains to a tantalum or tungsten target-copper alloy backing plate assembly capable of enduring high power sputtering, and to a production method therefor. Moreover, tantalum or tungsten as described in this specification shall include alloy targets having such components as the principal components.
Diffusion bonding is an effective method as a bonding method of a sputtering target and backing plate capable of surviving high power sputtering, and the present applicants presented in Japanese Patent Laid-Open Publication No. H6-108246 a solid phase diffusion bond target assembly in which an insert material is inserted between the target and backing plate, and a production method thereof. The sputtering target assembly produced with this solid phase diffusion bonding has superior adhesiveness and strength.
Nevertheless, the sputtering target itself is being enlarged pursuant to the enlargement of the wafer aperture in recent years, and, in particular, the deformation after the diffusion bonding is becoming a serious problem in a case where the thermal expansion coefficients of the target material and the backing plate material differ greatly.
When the thermal expansion coefficient of the sputtering target is smaller in comparison to the backing plate (this is often the case in a target-backing plate assembly structure), with the target on top and the backing plate on bottom, such sputtering target will curve convexly upward when it is cooled from the temperature of the diffusion bonding to room temperature, and, when the diffusion bonding strength is weak, there are cases where such sputtering target will separate from the outer periphery of the bonding boundary.
Moreover, even if it did not separate, the amount of curvature would become large, and, in order to prescribe the thickness of the target, it is necessary to process (cut) the convex portion of a target previously thickened for the amount of curvature or to correct the curve at room temperature after the diffusion bonding. This would cause a problem of increasing the work process and ultimately increasing the cost.
In particular, with targets prepared with the powder metallurgical production method such as with tungsten, there would even be incidents where the target would crack if the amount of curve is too large.
As case examples having this kind of problem, it has been confirmed that this problem occurs frequently when tantalum or tungsten is used as the target material and aluminum or aluminum alloy is used as the backing plate.
Further, there were even cases where the coolant would leak as a result of the backing plate deforming due to the thermal influence of high power sputtering.
For example, upon diffusion bonding a tantalum target having a xcfx86 of 350 mm and a thickness of 10 mm with an aluminum alloy (A5052) backing plate in a vacuum, at 500xc2x0 C. and bearing of 15 kgf/mm2, the amount of curvature varied between 4 mm to 7 mm per lot, and in some cases the bonding boundary had separated.
And, upon processing a bonded assembly having a curvature of 4 mm into a shape of a target and performing sputtering thereto at a sputtering power of 20 KW, the target deformed and an accident of water leakage was observed.
An object of the present invention is to provide a tantalum or tungsten target-backing plate assembly which suffers only a small deformation after the diffusion bonding even when the target material and the backing plate differ greatly in the thermal expansion coefficient, is free from separation between the target and the backing plate or from cracking, and capable of surviving high power sputtering; and a production method therefor.
Thus, upon conducting an intense study in relation to the production of a tantalum or tungsten target diffusion bonded with a backing plate capable of surviving high power sputtering and having a minimal amount of curvature after the diffusion bonding, the present inventors have discovered that it is extremely effective to use copper alloy, which has a smaller thermal expansion coefficient than aluminum alloy, which is hard and difficult to deform, and which has favorable thermal conductivity, as the backing plate, and to use an aluminum- or aluminum alloy-sheet having a certain degree of thickness as the insert material. Based on the foregoing discovery, the present invention provides:
A tantalum or tungsten target-copper alloy backing plate assembly characterized in that a tantalum or tungsten target and a copper chrome alloy or copper zinc alloy backing plate are subject to diffusion bonding via an aluminum- or aluminum alloy-sheet insert material having a thickness between 2.0 mm or more and 6.0 mm or less, and which is provided with diffusion bonded interfaces between the respective materials, wherein the amount of curvature after bonding is 3 mm or less.
A production method of a tantalum or tungsten target-copper alloy backing plate assembly, characterized in that a tantalum or tungsten target and a copper chrome alloy or copper zinc alloy backing plate are subject to diffusion bonding via an aluminum- or aluminum alloy-sheet insert material having a thickness between 2.0 mm or more and 6.0 mm or less in a vacuum, at a temperature between 400xc2x0 C. and 548xc2x0 C., and under a pressure condition of 15 to 20 kg/mm2, wherein the amount of curvature after bonding is 3 mm or less.